INTRODUCTION 



The f lammability of logging slash depends largely on its physical properties such 

 as fuel volume, surface area, weight, porosity, and size distribution of particles. 

 Quantitative knowledge of these properties will aid in understanding and predicting 

 fire behavior in slash. However, quantitative information describing many of the physi- 

 cal properties of slash is lacking, especially in regard to vertical distribution of 

 volume and surface area. 



Presented in this paper are results of a study that quantitatively determined fuel 

 volume, surface area, bulk density, and the ratio of void volume of fuel complex to 

 fuel surface area (A) at different vertical levels within logging slash. Also dis- 

 cussed are loading (weight per unit area) , percent composition of slash by particle 

 sizes, existence of suspended needle mats, and methods of measurement. 



This study is part of a fire research effort to quantitatively describe the prop- 

 erties of fuels and develop a means of relating these fuel properties to fire behavior. 

 As this knowledge accumulates it will be used to formulate and improve a system for 

 quantitatively appraising forest and range fuels. 



Major findings of the study were: 



1. Volume, surface area, and bulk density decrease from the ground up. Slightly 

 over two-thirds of the total volume and surface area was in the lower half of the slash. 



2. The total material in small-sized slash is distributed vertically in approxi- 

 mately the same proportions as in all-sized slash. 



3. Aging of slash for 6 months to 1 year greatly reduced the amount of needle 

 volume and surface area. 



4. An average of 80 percent of the total slash volume in the study was comprised 

 of material over 10 centimeters in diameter; this material would probably contribute 

 relatively little energy to rate of spread and intensity of a fire front. 



5. Mats of needles frequently were suspended in the slash and probably contribute 

 to the f lammability of aged slasfi. 



METHODS 



The area^ chosen for study had been clearcut and was located on the Tally Lake 

 Ranger District, Flathead National Forest. Trees in the study area (marked off in 10- 

 acre blocks) were mostly Douglas-fir {Pseudotsuga menziesii (Mirb.) Franco), Engelmann 

 spruce {Pioea engelmannii Parry), and western larch (Larix ocoidentalis Nutt.). Eight 

 blocks were selected so that north, east, south, and west aspects were equally repre- 

 sented; the blocks were sampled in July 1968. Also, the blocks were selected to furnish 

 two age classes of slash separated by 4 to 7 months (table 1) . Slash on different 

 aspects and of different ages was sampled to increase the range of conditions examined 

 and not to isolate the effects of aspect and age on the fuel properties. 



The physical fuel properties were determined separately (from ground to top of 

 slash) for 20-centimeter thick horizontal strata. A planar intersect technique, a 



^This area is the site of a cooperative study on the use of fire in silviculture; 

 cooperating in the study are the USDA Forest Service, Northern Region and Intermountain 

 Forest and Range Experiment Station. 



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